1. Field of the Invention
The present invention relates to a laser intensity adjusting method to be applied to an electrophotographic digital image forming apparatus of a digital copying apparatus, a digital printer or the like. More specifically, the present invention relates to a laser intensity adjusting method of adjusting the maximum intensity of laser light for irradiating the photoreceptor presenting a uniform potential given by the corona discharger, such that the potential of a photoreceptor portion exposed to laser of the maximum intensity is equal to a predetermined set potential.
2. Description of Related Art
In an image forming apparatus of a digital copying apparatus or the like, there is conducted, regularly or as necessary, a so-called potential correction for making correction such that the potential of the photoreceptor surface is equal to a predetermined value. The potential correction includes a so-called dark potential correction and a so-called residual potential correction. The dark potential correction refers to correction in which, with the photoreceptor not exposed to laser, the potential is corrected by adjusting the bias voltage of the grid of the corona discharger. The residual potential correction refers to correction in which, with the photoreceptor exposed to laser, the potential is corrected by adjusting the maximum intensity of the laser light. Generally, residual potential correction is to be conducted in succession after dark potential correction.
FIG. 4 schematically illustrates the arrangement of an image forming apparatus A of a color digital copying apparatus, in the vicinity of the photoreceptor thereof.
The image forming apparatus A has at its center a drum-like photoreceptor 1. Disposed around the photoreceptor 1 are a corona discharger 2 for giving a predetermined uniform potential to the surface of the photoreceptor 1, a laser exposure unit 8 (of which laser light is shown by an arrow of L) for causing a surface portion of the photoreceptor 1 to be exposed to the laser light based on an image read by an image reading device (not shown), a potential sensor 3 for measuring the surface potential of the photoreceptor 1, developing units 4a–4d for developing an electrostatic latent image on the surface of photoreceptor 1 formed by its exposure to the laser light of the laser exposure unit 8 (the developing units 4a–4d arranged to respectively form toner images of yellow, cyanogen, magenta and black), a transferring belt 5 for transferring, to transfer paper, the toner images on the photoreceptor 1 surface formed by the developing units 4a–4d, and a cleaning unit 6 for cleaning residual toner remaining on the photoreceptor 1 surface. These component elements above-mentioned are disposed in this order in the rotational direction of the photoreceptor 1 or in the direction of an arrow Y1.
The following description will discuss the operational procedure of dark potential correction and residual potential correction with reference to FIGS. 5 and 6.
At the dark potential correction (Step S51), the bias voltage of the grid of the corona discharger 2 is set to an optional value, and the potential (dark potential) of the photoreceptor 1 surface is measured by the potential sensor 3 with the photoreceptor 1 not exposed to the laser exposure unit 8. Based on a difference between the measured dark potential and the desired preset potential, using a relationship equation (linear equation) obtained through experiments or the like, the bias voltage is adjusted such that the dark potential is equal to the desired preset potential. The dark potential correction is relatively readily conducted in the manner above-mentioned because the relationship between the grid bias voltage and the surface potential of the photoreceptor 1 can be approximated using a substantially straight line function.
In succession, residual potential correction is to be conducted on the photoreceptor 1 which has just been subjected to dark potential correction. The maximum intensity of the laser exposure unit 8 is set to an optional value (for example {circle around (1)} in FIG. 6), and then the surface of the photoreceptor 1 presenting a uniform potential given by the corona discharger 2 is exposed to the laser light of the laser exposure unit 8 (Steps S52 and S53). Then, the potential (residual potential) of the photoreceptor 1 surface is measured by the potential sensor 3 (Step S54). A linear equation ({circle around (3)} in FIG. 6) previously obtained through experiments or the like is then applied to the measured residual potential ({circle around (2)} in FIG. 6) to calculate the laser intensity ({circle around (5)} in FIG. 6) for the desired preset potential ({circle around (4)} in FIG. 6) (Step S56). The laser intensity thus obtained is set as the maximum intensity (Step S57), and the operations of steps S53–S57 are repeated until the residual potential obtained at the step S54 becomes substantially equal to the desired preset potential (Step S55).
The foregoing conventional residual potential correction is disadvantageous in view of much labor and time required. More specifically, according to the conventional residual potential correction, the solution is searched using a linear equation previously obtained through experiments or the like. However, the actual relationship between laser intensity and residual potential is as shown in FIG. 6, and it is therefore difficult to linearly approximate this relationship. Thus, although the laser maximum intensity is gradually converged to the solution by repeating the steps S53–S57, repeated operations are required in a large number of iteration times before the final solution is obtained.